Walkthrough by G&D Productions.
Lara just got out of the sinking sub, quickly grab the small medipack and Flares, then swim straight to the back of the cave (no air here). Avoid contact with the two sharks and when you see the hull of a shipwreck, go right and just behind that anchor is a hole down, go in and around the corner swim up for air. Climb out of the water and behind those crates are Shotgun ammo and Harpoons (you have the Harpoon gun in the inventory).

From the floor shoot the shark(s) in case they followed you in.

For a Secret: Swim back through the opening you came from, from coming up at the anchor, go diagonally to the right and a bit right around that big rock pillar to the wall, left and down into a small tunnel in the rock pillar against the wall and get a Medipack and Secret #1, the Gold Dragon. Swim back fast and two Frogmen show up, quickly get onto the floor and shoot them.

Dive back in and swim under the floor, left through the opening and another Frogman probably shows up. I returned to the crates room and shot him from the floor. Swim back to that big room and up left in the back is a small opening to the next room, go immediately down and throw the underwater lever to open a hatch in the ceiling (you could go back for air now if you are below half full)

Up through the ceiling twice to get to a cargo hold with crates. Swim left through the opening to the next section and then swim right to the far back and up at the ladder is air. Climb out and in the dark corner a Thug will attack (drops a small medipack), pull the lever to drain the cargo hold.Climb down the ladder.

For a Secret: Don’t go down the ladder, but drop down onto the crates next to it, jump around the corner onto the other crate and go left. Careful; run jump in to the right or left, avoiding the trapdoors in front of the entrance. Grab Secret #2, the Silver Dragon and jump back out, get down to the floor.

Go to the other side and use the crates to jump over into the next section. Left, in the back, you can use the crates again to get to the opening in the wall.

Slide down into shallow water, to the other end and right around the corner into a large machine room.

For a Secret: In the middle is a structure with crates in small openings. There’s one you can pull out, in the back, so go around and get the crate out and aside. Inside climb up the crates and find the Uzis on the crates on the other side, jump to the top crate and go up through the opening in the ceiling. A Thug shows up, he will leave a small medipack. Be careful there are burner tiles in this room and if you step on those it is game over. Go to the side where you see pipes on the wall, the wall is climbable (turn right from where you climb up). Climb up and traverse to the right, back flip behind the pillar and use the lever (1) there to open a door Get the Uzi clips from the floor. Get back down by just hopping back and grab the edge, drop onto the crates and go down, out of the room and straight to the back wall. Left and into the passage, notice the door (2) and go left. You’ll get a screen of a sub; in the end of this part is the door you opened (1). Jump through and shoot the Thug, get the Harpoons from him and some extra on the floor and hop into the water, get ready to shoot the two Frog men. Grab Shotgun ammo from the bottom and in the back (the sub is gone) is Secret #3, the Jade Dragon. Get back out and to the large room where you pulled the crate.

Levers and Timed Doors.

On the back wall is a lever opening a door somewhere else, turn around and go left towards that passage, behind the barrels in the corner left is a small medipack. A Thug shows up, shoot him and go into that passage, up left is a door (3) for later. Go right around the corner and in the back straight ahead is that open door. Inside is a Timed lever, opening door (2). Run out, straight to the end with running jumps and left, with running jumps straight across to that small ramp and jump up right into door 2. Inside is also a Timed lever opening door (3), run out waiting for the door to open and go left, straight into the opposite passage and jump up left into the open door (3). Pick up the Flares and use the lever to open the door next to the first lever. So go out and right, then right into that door. A Thug shows up from behind, shoot him and get the Shotgun ammo.

Climb up the ladder in the back of the passage and run onto that trapdoor and fall into water. Collect Shotgun ammo and Uzi clips before you climb out at the other side. Follow the winding passage and shoot a Thug.

In the far opposite corner of the large machine room are Uzi clips, turn around and walk a bit back over the rusty ledge, turn a bit left at from the edge of it and run jump with a roll onto the edge of the higher slope you see there, immediately jump again without Ctrl and you should land on a higher block near where you got the Uzi clips. Turn around and spot a Medipack in a niche, jump there to get it and jump back. Jump and grab the next higher block and go right. Slide down and climb the ladder, off into the niche right to get Shotgun ammo. Back up the ladder and back flip (with roll) into the passage there. Safety drop down and shoot the two Thugs, the one with the gun leaves Shotgun ammo.

The lever there will open the door across the room, and two more Thugs come in. Go through to the Sub to leave this place.